Heat-treating apparatus



y 1944' R. P. KOEHRING 2,354,523

HEAT TREATING APPARATUS Filed April 22, 1941 11v VENTOR Roland F/(aelu'l'n Y 4 Z A TTOR Y5 Patented July 25, 1944 UNITED STATES iiATENTOFFICE HEAT-TREATING APPARATUS Roland 'P. Koehring, Dayton, Ohio,assignor to General Motors Corporation, Detroit, Mich; a

corporation of Delaware The present invention relates to heat treatingfurnaces and is particularly concerned with the heat treating furnacesof the bell type.

An object of the invention is to provide an apparatus for sintering andheat treating metal parts wherein the metal parts are rotated relativeto the walls of the furnace for equalizing the temperature of the metalparts.

In carrying out the above object it is a further object to provide atable within the furnace which is rotatable with respect to the furnacewhich table includes portions thereof relatively rotatable thereto andat different rates of speed whereby articles placed on said portions arerotatable relative to the table and the table is rotatable relative tothe furnace.

A further object of the invention is to provide a planetary system foruse in heat treating furnaces wherein articles may be placed on oneportion of the system, which portion is rotated upon its own axis whilesimultaneously being rotated in an orbit around the center of thefurnace.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing wherein a preferred embodiment of the present invention isclearly shown.

In the drawing:

Fig. 1 is a cross sectional view of a bell type furnace including theinvention disclosed herein and taken on the line |l of Fig. 2; and

Fig. 2 is a view taken on the line 2-2 of Fig. 1.

When heat treating metal parts in hell type furnaces, it is oftenimpossible to obtain equal heating of the parts being treated due to thefact that certain surfaces thereof are heated by radiated heat whileother surfaces must depend upon conducted heat. Similarly thetemperature at one side of the furnace may be much higher than thetemperature on the other side of the furnace thereby creating a spottyheat distribution which is very undesirable. Uniform heating isparticularly desirable during sintering of porous metal parts wherein ashort time sintering period is utilized during which period alloying andsometimes bonding of the porous metal to a steel supporting surface mustbe accomplished. In sintering porous metal parts, for example, annularclutch discs which include a steel backing having a briquetted powdermetal layer thereon it is customary to pile these discs or plates upon apilot within the furnace so that a plurality of plates are in the pileand each of the plates is under the desired pressure which may beapplied to the top of the pile. It is obvious that if the heatdistribution in a furnace of this type is uniform that a better bondwill be accomplished and with greater uniformity and strength.

This invention is particularly concerned with eliminating these pastdifiiculties in obtaining uniform heating of parts such as discs orother metal parts to be sintered or otherwise heat treated within a belltype furnace. To this end it is proposed to utilize a planetary heatequalizing apparatus wherein a plurality of piles of discs may be placedWithin the furnace and since the discs are moved relative to the heatingsurfaces to obtain uniform heat distribution, it is immaterial whetheror not each disc is equidis taut from the heating element whichobviously is a limiting factor in apparatus used prior to my inventionwhereby only one pile of discs could be sintered at one time.

Referring particularly to Fig. l, a bell type furnace 20 is shown whichincludes electrical heating elements 22 around the walls conforming tothe shape thereof, these maybe connected to suitable power source 24,gas heating may be employed if desired in any well-known manner. At thelower end of the furnace a rotatable table 25 is shown which carries agear 22% that is driven from a gear 30 attached to a suitable motivatingmeans, not shown. Thus the rotatable table 26 is rotated slowly relativeto the furnace heating surfaces. A plurality of vertically extendingpilots 32 are provided which are journaled on the table and arerotatable with respect thereto. Each pilot has a gear 34 adjacent thebottom thereof which meshes with a central gear 36 which is stationary,being mounted on a shaft 38 that is pinned by pin 48 to the base section42 of the furnace. Thus as gear 3ll turns the table 26, each of thepilots 32 are rotated relatively to the table by the action of the gears34 and 36. In this manner, the pilots simulate planets into a planetarysystem which rotate on an orbit at a given speed determined by the speedof the table 26 and which rotate on their own axis at a different rateof speed. Upon the pilots 32 may be stacked a plurality of plates 44which in the present are clutch plates although it is obvious that anyother flat article may be stacked upon the pilot or if the articles arenot annular they may be stacked upon the table carried by gears 34.Pressure may be exerted to the stack of plates by the addition of aweight on top thereof or by spring means, not shown, such expedientsbeing well known. The plates 44 may be spaced one from the other by alayer of alundum or by thin graphite sheets or by a layer of graphite sothat adjacent plates do not stick together during sintering.

When sintering porous metal parts it is also desirable that theatmosphere within the furnace is non-oxidizing in nature, suchatmospheres as incompletely burned natural gas, hydrogen atmosphere,cracked ammonium atmosphere, etc. being satisfactory. The furnace issealed to the air by means of the annular passage 46 in the base 42.This passage is filled with sand 48 or high boiling point oil and whenthe bell furnace is lowered therein the lower edge thereof effectivelyseals the inside of the furnace from the atmosphere. The nonoxidizinggas is admitted to the furnace through a pipe 50 whereby the pressureinside the furnace is maintained in excess of the atmospheric pressure;a slight leakage through the seal preferably results.

When sintering porous metal parts it is desirable to carry out theoperation under suitable sintering temperatures which temperatures aregenerally intermediate the melting points of the component metals to besintered, for example, if a bronze clutch plate is to be sintered asintering temperature intermediate the melting point of copper and tinmay be used preferably between 1500 to 1700 F. Similarly ifcopper-nickel powder comprises the briquetted powder metal layer,sintering temperatures between the melting points of copper and nickelis maintainedfor example, in the neighborhood of 2000 F.-2050 F. ispreferable. When sintering a single metal powder, such as iron powder,it is preferable to carry out the sintering operation at a hightemperature but below the melting point of the metal. In the case ofiron it has been found that a temperature of about 2050 F. issatisfactory. In each case the metal powder is preferably briquettedprior to sintering and a wide range of pressure may be used for thisstep, for example, from 10,000 to 70,000 pounds per square inch. Ifadditional pressure is applied to a stack of plates during sinteringthereof it is possible in some cases to use loose metal powders whichare supported upon a sheet of steel or the like in a layer of definedthickness which upon sintering is compressed due to the pressure appliedto the stack. The compression improves the bonding between the powderedmetal layer and the steel and likewise reduces the porosity of theporous metal layer.

It is obvious that porous metal layers which are not bonded to steel maybe sintered in a like manner.

The foregoing examples have been given for illustrative purposes only.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

1. Apparatus for heat treating a plurality of stacked annular platescomprising in combination; a removable bell type furnace cover,electrical heating means disposed adjacent the internal verticalsurfaces of said cover, a rotatable table member adapted to be enclosedby said cover, a pilot carried by said table member and relativelyrotatable with respect thereto, said pilot being adapted to carry astack of said annular plates to be heat treated; means for rotating thetable member and the pilot at different rates of speed whereby differentsurfaces of said plates are exposed to the heating surfaces of thefurnace, and means for introducing a controlled atmosphere into saidfurnace for preventing oxidation of said plates said means beingdisposed so as to direct the flow of controlled atmosphere over saidmeans for rotating the table whereby said means is maintained at atemperature less than the heat treating temperature.

2. Apparatus for heat treating a plurality of stacked annular platescomprising in combination; a removable bell type furnace cover,electrical heating means disposed adjacent the internal verticalsurfaces of said cover, a rotatable table member adapted to be enclosedby said cover, a plurality of pilots carried by said table member andrelatively rotatable with respect thereto, said pilots being adapted tocarry stacks of said annular plates to be heat treated; means forrotating the table member and pilots at different rates of speed wherebydifferent surfaces of said plates are exposed to the heating surfaces ofthe furnace, and means for introducing a controlled atmosphere into saidfurnace for preventing oxidation of said plates said means beingdisposed so as to direct the flow of controlled atmosphere over saidmeans for rotating the table whereby said means is maintained at atemperature less than the heat treating ternperature.

ROLAND P. KOEHRING.

